Note that the points discussed below may reflect the hindsight gained from the disclosed inventions, and are not necessarily admitted to be prior art. Increasing number of people want to use mobile phones for both voice and data services. They want to access those services wherever they are, including in their home residences. However, to provide full and sufficient mobile coverage is always challenging for the mobile operators, and many times the mobile coverage in the home may be poor. To provide better coverage, the mobile operators need to add more base stations, which may not be economical due to the high cost of the base station and the revenue that it generate in the coverage area.
To solve this problem, the industry has introduced the concept of a femtocell. Originally called an access point base station—a scalable, multi-channel, two-way communication device extending a typical base station by incorporating all of the major components of the telecommunications infrastructure. Application of VoIP techniques allows such a unit to provide voice and data services in the same way as a normal base station, but with the deployment simplicity of a Wi-Fi access point.
A cheap, small capacity femtocell base station can be installed in a subscriber's home. Femtocell base stations provide full 3G base stations with low transmission power and use an already-existing fixed line as the backhaul path, saving the cost from the expensive ATM backhaul. Since it is using the 3G base station technology, a femtocell base station allows the existing handsets to work without any changes, e.g. without the support of Wi-Fi at the handsets. In summary, femtocells extend the mobile coverage to residential homes and replace the expensive backhaul link with cheap broadband connection, without the need to modify the handsets.
In the radio access network, the governing element is an RNC (radio network controller) that is responsible for radio resource management. The RNC connects to a circuit-switched core network through a media gateway (MOW) and to an SGSN (serving GPRS (general packet radio service) support node). The logic connections between the network elements, known as interfaces, are shown in FIG. 1. The interface between the RNC and the circuit switched core network (CS-CN) is called lu-CS and between the RNC and the packet switched core network is called Iu-PS. Other interfaces include lub (between the RNC and the node-B) and Iur (between RNCs in the same network). Iu interfaces carry user traffic (such as voice or data) as well as control information, and lur interface is primarily used for soft handovers.
Since the femtocell device typically contains all the telecommunication elements such as a Node-B, RNC, and GSN with only an Ethernet or broadband connection to the Internet or an intranet, the supporting interfaces need to be encapsulated in IP and transported to suitable entry point in the operator's network.
Several architectures are possible to support femtocell operations, depending on the capability of the femtocell base stations and the corresponding core network node.
Several examples are as follows:
lub over IP: A femtocell base station supports 3G radio base station functionalities and is connected to the radio network control (RNC) node. Iub interface is supported between the femtocell base station and the RNC. This is typically a less open single vendor solution, and usually femtocell base stations and RNCs are bundled.
Iu-CS/Iu-PS over IP: A femtocell base station supports 3G base station and RNC functionalities, and it is connected to the MSC and SGSN in the core network. lu-CS and lu-PS interface is supported between femtocell base station and the MSC (mobile switching center) and SGSN, respectively. This configuration has the advantage of reducing one node from the user plane.
SIP (Session Initiation Protocol) method: SIP provides a signaling and call setup protocol for IP-based communications that can support a superset of the call processing functions and features present in the public switched telephone network. In a SIP based femtocell, all the core network functionalities (including RNC, SGSN, and GGSN (Gateway GPRS Support Node (GGSN)) are collapsed into the femtocell base stations, and the femtocell base station terminates all the Non Access Stratum (NAS) messages.
In an SIP based femtocell architecture, pure IP packets are produced from femtocell base stations and all the services are provided via SIP. This architecture provides the framework for all-IP network and services and is a desirable architecture. However, the femtocell base stations need to provide most functionality support for all the services, in particular, the femtocells are required to perform the voice call control to SIP translation for voice traffic.
Even though these mechanisms extend the coverage to residential homes and replace the expensive backhaul with an IP network, they still utilize the 3G signaling (i.e., lub or lu-CS/Iu-PS) although enwrapped in IP. The non-IP payload transfer over IP is not an efficient way of handling data applications for the femtocell design.
The reuse of existing RAN technologies (and potentially re-use of existing frequency channels) could also create problems, since the additional femtocell transmitters represent a large number of interference sources, potentially resulting in significant operational challenges for existing deployments.
Also femtocell technology typically relies on the Internet for connectivity, which although reduces deployment costs but introduces security risks that generally do not exist in typical cellular systems.
A more efficient and secure way of communication interface is needed for the success deployment of femtocell network architecture.